Many vinyl compounds are polymerizable by free-radicals. Examples include acrylates and methacrylates, acrylamides and methacrylamides, allyl ethers, and styrenes.
Free-radical polymerization of vinyl compound(s) using certain beta-dicarbonyl (i.e., 1,3-dicarbonyl) compounds in the presence of a peroxide and/or molecular oxygen, a halide salt, and a copper compound such as copper acetylacetonate, has been described in U.S. Pat. No. 3,347,954 (Bredereck et al.). Such compositions cause free-radical polymerization of the vinyl compound(s) over time, with shorter times generally being preferred. Since the compositions are spontaneously reactive, it is common practice to provide them as a two-part system such as, for example, a part A and a part B that are combined immediately prior to use.
Organocopper compounds such as copper acetylacetonate may contain copper in a +1 or +2 oxidation state, and typically have good solubility in many organic systems. However, a typical problem of including such copper compounds in curable compositions is that they are prone to color formation, and may not be suitable for use in applications where absence of color is desirable for aesthetic and/or functional reasons.
Air-activated initiator systems are useful for polymerizing acrylic monomers in applications where oxygen-inhibition of the polymerization reaction is a concern. Two-part acrylic structural adhesives and liquid optically clear adhesives (LOCA) present specific examples where oxygen inhibition produces an undesirable tacky surface.
It would be desirable to have new methods for curing air-activated free-radically polymerizable systems such as, for example, those described above, especially if they provide extended shelf life prior to curing on a substrate.